The present invention is directed to a motorized vehicle, such as an industrial pallet truck, that the operator can ride on or walk alongside of. An industrial pallet truck is utilized to lift and transport loads between locations. Loads may be transported from aisles in warehouses, truck trailers, and in retail stores, for example. The conditions for transporting and maneuvering the loads will vary greatly depending on the location and the size of the load. As such, the operator will need to constantly adjust not only the steering of the pallet truck as a whole, but also the angle of the control arm, and the acceleration, deceleration, travel speed and direction of the motorized vehicle. Maneuvering the pallet truck requires careful attention of the operator, and typical operation involves guiding the pallet truck in a wide variety of stacking and steering maneuvers, which requires significant operator expertise to avoid obstacles, position a load, and turn in narrow confines. Further, the steering effort to maneuver the motorized pallet truck is dependent upon the angle of the control arm, the steering angle, and the load carried by the vehicle. As an example, the steering effort for a typical motorized pallet truck carrying a capacity load of 8,000 pounds can exceed 100 pounds.
Typical pallet truck steering systems and direction/speed control systems regulate the acceleration, deceleration, braking, and travel speeds of the motorized vehicle as a function of the vertical position of the control arm. Most steer systems utilize a simple on/off switch to detect the steering tongue position either in the brake “on” or “off” positions, where an approximate vertical position and approximate horizontal position of the control arm are considered the braking positions, or brake “on” position. Control arm positions intermediate the approximate vertical and approximate horizontal positions are considered the non-braking position, or brake “off” position, and allow for vehicle acceleration.
Some pallet truck steering systems provide that as the control arm approaches the vertical and horizontal positions, the level of performance of the traction system is reduced to a lower value so as to avoid abrupt changes in travel speed. These systems recognize that when the control arm is in a near vertical position that the operator is likely maneuvering the pallet truck in a narrow confine, and requires more sensitive control for steering and acceleration. By causing a reduction in the overall level of performance of the traction system, the operator is able to control the speed and steering of the truck in finer increments while using the same throttle control as at normal travel speeds. A dead-man switch such as those known in the state of the art, disables the traction system when the control arm is moved to either the vertical or horizontal position.
With the control arm moved from the vertical position, the pallet truck will move in a forward or reverse direction according to the direction control sent by the throttle. With the control arm located in a central position, along the axis of the pallet truck centerline, the pallet truck is in its most stable configuration, and the truck may be accelerated at the maximum value. However, as the control arm is turned towards the left or right steering positions, lateral stability of the pallet truck becomes increasingly compromised the further the control arm is turned towards the extreme left and right steering positions. At the extreme left and right positions, the control arm is positioned nearly perpendicular to the centerline axis of the pallet truck that lies parallel with the forks, and therefore provides the smallest turning radius possible. In this condition, the pallet truck is least stable from a lateral perspective, and sudden, rapid increases to the output of the traction system can cause the pallet truck to pivot onto the side of the frame, and potential damage the pallet truck, the floor, or the load. Inappropriate levels of acceleration might be the result of improper techniques from less experience operators, or for maneuvers involving large loads, for example.
Typical pallet trucks utilize a control arm that is manually operated, however this can result in a manual effort by the operator of as much as 100 lb of force to turn the control arm when a heavy load is being transported, contributing to unwanted operator fatigue. Power assisted steering systems used in some industrial vehicles attempt to overcome this problem by detecting a threshold torque applied by the operator on the steer device, and then provide assisted power steering by means of an auxiliary steer motor or hydraulic device.
It is desirable to control the level of performance of the traction system and power assist steering system not only as a function of the control arm angle from a vertical to horizontal position, but also as a function of steering position from left to right. It is also desirable to measure the rate of change of the position of the control arm, such that the acceleration, deceleration, braking, travel speed, and power assisted steering may be modulated according to the operator's command. The present invention addresses these and other problems associated with the prior art.